Bicycle with suspension

ABSTRACT

A bicycle can include a suspension system with a shock absorber. The shock absorber can have a sag position which can be adjustable. Sag refers to the amount of movement experienced by the suspension under a static load, such as that of the weight of a rider. Methods and systems to set sag can include at least one valve in fluid communication with a gas chamber of the shock absorber. In some embodiments, the at least one valve can be used to automatically set the sag position based on an individual&#39;s weight and riding position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/670,233, filed Aug. 7, 2017, which is a continuation of U.S.application Ser. No. 15/143,209, filed Apr. 29, 2016, which is adivisional of U.S. application Ser. No. 13/607,470, filed Sep. 7, 2012,which is a divisional of U.S. application Ser. No. 12/833,745, filedJul. 9, 2010. Each of the foregoing applications is hereby incorporatedby reference herein in its entirety and is to be considered a part ofthis specification.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to bicycle suspension systems.In particular, the present invention relates to shock absorbers andsuspension assemblies suitable for use in connection with off-roadbicycles.

Description of the Related Art

Off-road bicycles, or mountain bikes, may be equipped with front andrear suspension assemblies operably positioned between the frame of thebicycle and the front and rear wheels, respectively. Providing front andrear suspension on a mountain bike potentially improves handling andperformance by absorbing bumps, and other rough trail conditions, whichmay be encountered while riding off-road. However, because mountainbikes are typically pedal-driven, i.e., use the rider's power output topropel the bicycle, the provision of rear suspension, especially, mayundesirably absorb a rider's power output, resulting in wasted effort.

Accordingly, rear suspension systems commonly incorporated onengine-driven vehicles, such as motorcycles, have proven undesirable foruse with pedal-driven vehicles, such as mountain bikes. In addition,because a mountain bike is propelled solely by power output from therider, it is desirable that the rear suspension assembly be lightweight.Rear suspension systems of engine-driven vehicles commonly emphasizestrength over weight and, therefore, have not been widely incorporatedon mountain bikes.

Bicycle shock absorbers having rider-adjustable compression and rebounddamping characteristics have been used to match a desired level ofpedaling efficiency and ride comfort with a type of terrain encountered.A rider may adjust the compression damping setting of a shock absorberto trade improved pedaling efficiency for improved bump absorption. Forexample, an adjustable shock absorber may desirably be set to a firmsetting while a rider is on a steep hill climb to increase the amount ofpedaling energy reaching the driven wheel and reduce the amount ofpedaling energy dissipated by the suspension. Conversely, an adjustableshock absorber may desirably be set to a relatively soft compressiondamping setting where a rider is traveling fast downhill.

In addition, many bicycle shock absorbers have other rider-adjustablesettings. For example, some bicycle shock absorbers allow the user toset the sag. Sag refers to the amount of movement experienced by thesuspension under just the static load, or body weight, of the rider.

All of these different adjustments can be overwhelming to a user,especially a less experienced rider. Not only do some shock absorbershave multiple adjustments but some adjustments require a specificprocedure that can be time consuming and difficult to perform.

For example, to set the sag on currently available air shock absorbers,a specific setup procedure, which can include multiple steps andadjustments, is required to ensure maximum performance. Generally, therider has to adjust the air pressure and the sag position multiple timesto achieve the desired sag when sitting on the bike. This includesmeasuring the shock absorber, filling the shock with air, sitting on thebike, measuring the sag, letting air out of the shock or adding moreair, getting back on the bike, and measuring the sag again. These stepsare repeated until the sag is set to the desired position.

The desired sag position may be given in a chart in a user manual andindicated as a length or a sag percentage based on the particular shockand the rider's weight among other factors. This can further complicatethe procedure.

Because of the perceived difficulty of certain, if not all of theadjustments, some riders may have the shock absorber adjusted or set-upwhen it is originally purchased and then make no further adjustments. Inaddition, certain bike shops or consumers may not make all of the rightadjustments. This may be in order to save time or just because of lackof understanding of the correct procedure and settings.

Accordingly, a need exists for a shock absorber that simplifies at leastsome of the adjustment procedures.

SUMMARY OF THE INVENTION

A method of adjusting a bicycle suspension sag position can includemultiple steps. One step can be inflating a gas chamber of a bicycleshock absorber through a valve to a pressure value well exceeding thatrequired for a typical rider. Another step can be compressing the shockabsorber by a person is sitting on the bicycle in a riding position. Afurther step can be deflating the gas chamber through the valve whilethe person is sitting on the bicycle in the riding position until thedeflation automatically stops. In some embodiments, another step caninclude closing the valve.

Some methods can further include one or more of the steps, the persongetting off the bike and moving the valve to close a valve portcommunicating with the gas chamber.

A bicycle assembly according to certain embodiments can comprise a shockabsorber. The shock absorber can include a gas chamber, a movable pistonwithin the gas chamber, and at least one valve in communication with thegas chamber. In some embodiments, the gas chamber can be divided by thepiston into a first chamber and a second chamber, the first and secondchambers configured to be determined at least in part by the position ofthe piston within the gas chamber, and the at least one valve beingpositioned to communicate with the first chamber when in an uncompressedposition and communicate with the second chamber and not the firstchamber when in a compressed position.

In some embodiments, a shock absorber can comprise a gas chamber havingan interior surface, a movable piston forming a seal with the interiorsurface and configured to move along the interior surface, at least onevalve for inflating and deflating the gas chamber with fluid and atleast one valve port configured to establish fluid communication betweenthe gas chamber and the at least one valve.

In some embodiments, the gas chamber can be divided by the piston into afirst chamber and a second chamber, the first and second chambersconfigured to be determined at least in part by the position of thepiston within the gas chamber, and the at least one valve port beingpositioned to communicate with the first chamber when in an uncompressedposition and communicate with the second chamber and not the firstchamber when in a compressed position.

Some embodiments of shock absorber can include a bypass channel. Thebypass channel can be a groove along an interior surface of the gaschamber or another shape or feature.

In some embodiments of shock absorber the at least one valve port can bein communication with both the first and the second chambers. In someembodiments of shock absorber the at least one valve port can be alongthe interior surface of the gas chamber.

According to certain embodiments, a method of adjusting a bicyclesuspension sag position can comprise providing a bicycle having a shockabsorber, inflating a gas chamber of the shock absorber through a valveto a pressure of at least 250 psi; compressing the shock absorber by aperson sitting on the bicycle in a riding position; deflating the gaschamber through the valve while the person is sitting on the bicycle inthe riding position until the piston passes a valve port; and closingthe connection between the valve and a first changeable volume.

In some methods of adjusting a sag position, a shock absorber caninclude a gas chamber having an interior surface; a movable pistonforming a seal with the interior surface and configured to move alongthe interior surface; at least one valve for inflating and deflating thegas chamber with fluid; and at least one valve port configured toestablish fluid communication between the gas chamber and the valvealong the interior surface. The gas chamber can be divided by the pistoninto a first changeable volume and a second changeable volume, thevolumes configured to be determined at least in part by the position ofthe piston within the gas chamber, and the valve port can be along theinterior surface such that in a first position the valve is configuredto be in fluid communication with the first changeable volume and in asecond position the valve is configured to be in fluid communicationwith the second changeable volume. The method can include inflating thegas chamber of the bicycle shock absorber through the valve to apressure of at least 250 psi; compressing the shock absorber by a personsitting on the bicycle in a riding position; deflating the gas chamberthrough the valve while the person is sitting on the bicycle in theriding position until the piston passes the valve port; and closing theconnection between the valve and the first changeable volume.

In some embodiments a shock absorber can comprise a spring assembly. Thespring assembly can include a gas cylinder having an inner surface, apiston that engages the inner surface, a port and a bypass channel. Thegas cylinder and piston can define a gas chamber and a negative gaschamber, wherein the gas chamber is separated from the negative gaschamber by the piston. The port can provide access into the gas cylinderto adjust the pressure within the gas cylinder. The bypass channel canbe located at the port to permit fluid to bypass the piston to equalizethe pressure in the gas cylinder between the gas chamber and thenegative gas chamber.

In certain embodiments of the shock absorber, the port can be positionedalong the inner surface of the gas cylinder. The port may provide accessto the gas chamber in a first position of the shock absorber andprovides access to the negative gas chamber in a second position of theshock absorber

A shock absorber according to some embodiments can comprise a housing, aplunger, a port and a channel. The housing can have an internal walldefining an internal chamber, the internal chamber configured to receiveair and to act as an air spring. The plunger can be positioned withinthe internal chamber and sealingly engaging the internal wall, theplunger dividing the internal chamber between a first side and a secondside, each of the first and second sides defining an adjustable volumebased on the position of the plunger within the internal chamber. Theport can be in fluid communication with the internal chamber andconfigured to open and close to release air from the internal chamber.The channel can be in the internal wall, the channel shaped such thatwhen the plunger is positioned at the channel, air can communicatebetween the first side and the second side. The channel can bepositioned within the internal chamber at the same longitudinal positionas the port.

Certain embodiments of a method of setting sag on a bicycle can compriseone or more of the following steps. Over inflating a gas chamber of ashock absorber on a bicycle to an over inflated pressure exceeding afinal pressure for a typical rider, the shock absorber comprising a gascylinder divided between the gas chamber and a negative gas chamber by apiston. Deflating the shock absorber through a port in the shockabsorber until the deflation stops, while a user assumes a ridingposition on the bicycle. Closing the port. Passing the piston over theport after the user has dismounted the bicycle. Equalizing the pressurein the gas cylinder by permitting fluid to go around the piston in thegas cylinder at the port and flow between the gas chamber and thenegative gas chamber.

A method may further comprise one or more of the following additionalsteps. Equalizing a pressure within the negative gas chamber withatmospheric pressure before closing the port. Sealing the gas chamberfrom the negative gas chamber after equalizing the pressure. Attachingan air pump to a valve in fluid communication with the port. The airpump may be used to both inflate and deflate the pressure of the gaschamber.

In some methods deflating the shock absorber through the port in theshock absorber until the deflation stops can comprise passing the pistonby the port. Equalizing the pressure in the gas cylinder can comprisepermitting fluid to go around the piston in the gas cylinder at a bypassand flow between the gas chamber and the negative gas chamber.Equalizing the pressure in the gas cylinder can comprise passing thepiston over a groove in the gas cylinder. Over inflating the gas chambercan comprise inflating the gas chamber to a pressure of at least, 200,250, 300, or 350 psi; or to a pressure at least 20%, 30% or 40% over theapproximate typical final pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages are described belowwith reference to drawings of preferred embodiments, which are intendedfor illustration purposes only.

FIG. 1 illustrates a side view of an embodiment of a bicycle.

FIG. 2 is a perspective view of an embodiment of a shock absorber.

FIG. 3 shows a cross-section of the shock absorber of FIG. 2.

FIG. 3A shows another embodiment of a shock absorber in cross-section.

FIG. 4 is a flow chart illustrating a method of setting sag.

FIGS. 5 and 6 show a shock absorber during a method of setting sag.

FIGS. 5A-B and 6A are detail views showing fluid flow.

FIGS. 7 and 8 show another embodiment of a shock absorber during amethod of setting sag.

FIG. 9 is a detail view showing fluid flow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates an off-road bicycle, or mountain bike 10, including apreferred embodiment of a rear suspension assembly, or shock absorber.The bicycle 10 is described herein with reference to a coordinate systemwherein a longitudinal axis extends from a forward end to a rearward endof the bicycle 10. A vertical, central plane generally bisects thebicycle 10 and contains the longitudinal axis. A lateral axis extendsnormal to the longitudinal axis and lies within a horizontal plane. Inaddition, relative heights are generally expressed as elevationsrelative to a horizontal surface on which the bicycle 10 is supported inan upright position. The above-described coordinate system is providedfor the convenience of describing the bicycle illustrated in FIG. 1, andis non-limiting. In addition, certain features and components of thebicycle may be described in terms of relative positions or directionswithin the particular positions and orientations reflected in thedrawings, which is merely for convenience.

The bicycle 10 includes a frame 2, preferably comprised of a generallytriangular main frame portion 4 and an articulating frame portion, orsubframe 6. The subframe 6 is pivotally connected to the main frame 4.The bicycle 10 also includes a front wheel 8 carried by a frontsuspension assembly, or front fork 12. A steerer tube (not shown) isjournaled for limited rotation about a steering axis defined by the mainframe 4. The fork 12 is secured to the main frame 4 by a handlebarassembly 14, as is well known in the art. A rear wheel 8 of the bicycle10 is carried by the subframe 6. A shock absorber 20 is pivotallyconnected to both the main frame 4 and the subframe 6 to provideresistance to the pivoting motion of the subframe 6 and, thus, provideresistance to the suspension travel of the rear wheel 8.

In addition, a seat 16 is connected to the frame 2 by a seat post 18,which is received within the seat tube of the main frame 4. The seat 16provides support for a rider of the bicycle 10. A pedal crank assembly 3is rotatably supported by the main frame 14 and drives a multi-speedchain drive arrangement 5, as is well known in the art. The bicycle 10also includes front and rear brake systems 7 for slowing and stoppingthe bicycle 10. Although the front and rear brakes 7 are illustrated asdisc type brakes, alternatively, rim type brakes may be provided, aswill be appreciated by one of skill in the art. Rider controls (notshown) are commonly provided on the handlebar assembly 14 and areoperable to control shifting of the multi-speed chain drive arrangement5 and front and rear brake systems 7.

The shock absorber 20 is shown hydraulically connected to a fluidreservoir 9 with a connecting hose 11, though other configurations arealso possible including the absence of a fluid reservoir. The fluidreservoir can be similar to those shown in U.S. Pat. Nos. 6,267,400 and7,552,935, hereby incorporated herein by reference and made a part ofthis specification.

Shock Absorber

A shock absorber 20, shown in FIG. 2, can have a main shock body 22 andan eyelet 24 at either end. The shock absorber 20 can attach at theeyelets 24 to a bicycle frame 2 as part of a rear suspension, as shownin FIG. 1.

FIG. 3 is a cross-sectional view of the shock absorber 20 shown in FIG.2. The shock absorber 20 includes a main shock body 22 and may include areservoir 9 (FIG. 1). The shock absorber 20 includes a damping assembly30 and a spring assembly 40. The spring assembly 40 is preferablylocated within the main shock body 22. The damping assembly 30 can bewithin the main shock body 22 or divided between the main shock body 22and a reservoir 9.

The damping assembly 30 of the main shock body 40 shown in FIG. 3,desirably includes a tube 34 and a piston rod 26. The piston rod 26carries a piston or compression piston 28 in sliding engagement with aninterior surface of the tube 34. Thus, the piston rod 26 and piston 28are movable relative to the tube 34.

The interior of the tube 34 desirably defines a piston chamber and thepiston 28 further divides the interior of the tube 34 into a compressionchamber 32 and a rebound chamber 36. The piston 28 desirably includesthrough-ports 38 which permit fluid to flow between the compressionchamber 32 and the rebound chamber 36. However, as the piston 28 movesprogressively further into the tube 34, the piston rod 26 takes up anincreasing volume of the rebound chamber 36. That is, the reduction involume of the compression chamber 32 is greater than the increase in thevolume of the rebound chamber 36 (by an amount equal to the volume ofthe piston rod 26, or “rod volume”, introduced into the tube 34). As aresult, a reservoir 9 can be provided to accept the excess fluid thatcannot be accommodated by the rebound chamber 36.

Thus, the reservoir is preferably an accumulator that accepts excessdamping fluid upon compression of the shock absorber 20, and thenreturns the fluid to the main shock body 22 upon expansion or rebound ofthe shock absorber 20. Among other features, the reservoir 42 caninclude an inertia valve assembly and a position sensitive valveassembly, such as those described in particular in reference to FIGS.2-4, 6-15 and the accompanying description in U.S. Pat. No. 7,552,935,hereby incorporated by reference herein and made a part of thisspecification.

The piston 28 can include one or more axial compression passages 38 thatare covered on the end opening into the rebound chamber 36 by a shim orshim stack. The compression passages and shim or shim stack allows fluidto flow through these passages during compression but not duringrebound. During rebound, the fluid flows from the rebound chamber 52through an adjustable valve 52, located within the interior of thepiston rod 26 near the piston 28, and into the compression chamber 32.The flow rate through the valve 52 is controlled by an adjustment rod 54that is preferably connected to an external adjustment knob 56. Inaddition, other flow circuits between the compression and reboundchambers may also be provided.

Although the illustrated reservoir 9 in FIG. 1 is defined by a separatestructure from the main shock body 22, in other arrangements thereservoir 9 and shock body 22 may share common structural components.Furthermore, in some arrangements, a separate reservoir may not beprovided. Instead, the compression 32 and/or rebound 36 chambers may beconfigured to vary in volume to accommodate fluid displaced by thepiston rod 26. Other suitable compensation mechanisms may also be used.In addition, in some embodiments, the shock absorber 20 does not includea damping assembly.

The spring assembly 40 of the shock absorber 20 illustrated in FIG. 3preferably uses a compressed gas to bias the main shock body 22 towardan extended position. The compressed gas is stored in a gas chamber 42,which is defined by a tube, or gas cylinder 44. The gas chamber 42 canbe partitioned from the fluid filled compression and rebound chambers 36and 32 by an annular piston or spring piston 50. The piston 50 shown isin sealed, slidable engagement with both the piston shaft 26 and theinner wall of the gas cylinder 44. The illustrated piston 50 is shown astwo pieces but may be one integrated piece. The pressure of thecompressed gas may be adjustable by at least one valve 60 configured topermit communication with the gas chamber 42. FIG. 3A illustrates anembodiment with a first valve 60A and a second valve 60B. The two valvescan both or individually be used for filling and/or adjusting thepressure within the gas chamber 42. For example, in some embodiments,the valve 60A, shown with a schematic representation of a Schradervalve, can be used to fill the gas chamber 42 and then the valve 60B canbe used to adjust the sag position as will be described below.

During operation, the tube 34 is displaced along a longitudinal axis ofthe main shock body 22 into the interior of gas cylinder 44, whichreduces the volume of the gas chamber 42. This reduction of volumeincreases the pressure of the gas chamber 42 and thus increases thebiasing force tending to extend the main shock body 22. A compressed gasshock absorber is beneficial in that the biasing force of the compressedgas may replace that of a metallic coil spring, which results in areduced weight of the shock absorber 20.

The illustrated shock absorber 20 also includes a negative gas chamber46 defined between an end seal assembly 48 of the gas cylinder 44 andthe piston 50. The negative gas chamber 46 exerts a force which resistsexpansion of the shock absorber 20. This force preferably assists in theinitial compression stages of the shock absorber 20 and thus creates asmoother compression action.

As has been mentioned, a shock absorber can have various adjustmentmechanisms to change or set certain characteristics of the shockabsorber and how it responds under certain situations. One of theseadjustments can include sag.

Sag refers to how much the suspension moves under the static load orbody weight of the rider on the bicycle. The preload of a shock absorbercan generally be adjusted so that the desired sag is achieved. Preloadrefers to the force applied to the spring before external loads, such asrider weight, are applied. More preload makes the suspension sag less,and less preload makes the suspension sag more. Adjusting preloadaffects the ride height of the suspension.

It can be desired to have a certain sag percentage when the rider sitson the bike. Common values for the sag percentage are about 20-35%, itcan also be between about 5-45%, depending on the terrain, type ofriding and amount of travel of the suspension, among other factors.

For currently available air shock absorbers, a specific setup procedure,which can include multiple steps and adjustments, is required to ensuremaximum performance. Generally, the rider adjusts the air pressure andsag multiple times to achieve the desired sag when sitting on the bike.This includes measuring the shock absorber, filling the shock with air,sitting on the bike, measuring the sag, letting air out of the shock oradding more air, getting back on the bike, measuring the sag, thesesteps are repeated until the sag is adjusted to the desired position andcan take multiple rounds of adjustment.

It is desirable to provide an improved sag adjustment. Particularly, toprovide an adjustment that is easier for consumers and bike shops, whilealso providing an adjustment able to set the shock at the desired sagbased on the specific weight and riding position of the individualrider.

A shock absorber 20 can have a valve 60 that can be used toautomatically adjust the sag valve. The valve 60, according to someembodiments, can allow a rider to adjust the air pressure once in orderto achieve a proper sag percentage. FIG. 4 shows a method of setting sagand FIGS. 5-6 demonstrate the position of the shock absorber 20 atdifferent parts of the method. FIGS. 5A-B and 6A show the fluid flowrepresented by the arrows.

In a first step, S1, a shock absorber air pump 80 can be connected tothe valve 60 (FIG. 5). The valve 60 can have a Schrader or Presta stylevalve for connecting to the pump. In some embodiments, the valve 60 canhave threads 62 for receiving a cap 58 and also for threadedly receivingthe pump. Using the pump, the air pressure within the shock absorber 20can then be set to a value well exceeding that required for a typicalrider, or the typical final pressure (FIG. 5A). This can be the same forall riders, e.g. the owner's manual can instruct all users to inflatethe shock absorber 20 to a pressure of at least, 200, 250, 300, or 350psi, for example. In some embodiments, the shock pressure can be atleast 20%, 30% or 40% over the approximate typical final pressure. Thegas chamber 42 is now charged and is a positive chamber, that is, it hasa positive pressure within the gas chamber 42. The typical finalpressure can be between about 150-220 psi, or between about 100-240 psi.

In a next step, S2, a rider can sit on the bicycle in the ridingposition with his or her feet on the pedals. Air can now be releasedfrom the gas chamber 42 in the shock absorber 20 through the valve 60(FIG. 5B). As air is released, the pressure in the gas chamber 42 willdrop and the shock will compress due to the weight of the rider and thepressure drop. As the pressure drops, the piston 50 will slide withinthe gas chamber 42 decreasing the volume of gas chamber while increasingthe volume of the negative gas chamber 46. Once the piston 50 slidespast the port 64 the air pressure in the gas chamber 42 will no longerdrop as the port 64 is no longer in fluid communication with the gaschamber 42 (FIG. 6). As mentioned previously, in some embodiments a pumpcan be attached to a first valve 60A to fill the shock absorber and asecond valve 60B can be used to release the air (FIG. 3A), otherconfigurations are also possible.

Once the piston 50 is past the port 64, the negative pressure in thenegative gas chamber 46 will equalize to atmospheric pressure (FIG. 6A).The internal pressure of the shock absorber 20 is now setup specificallyfor the individual rider's weight and riding position. As the rider'sweight and riding position can help determine when the piston 50 willpass by the port 64 to prevent further pressure drop in positive gaschamber 42. Accordingly, in some embodiments, the sag setup is nowcomplete as the shock is now in the sag position for the individualrider.

The valve 60 can now be closed, S3, and the rider can get off the bike.The gas chamber 42 pressure can now be advantageously set to achieve adesired sag % for the specific rider. Under certain conditions, the sag% can be an ideal sag % for the specific rider.

According to some embodiments, a method of setting sag can includeincreasing air pressure within a shock absorber to at least 250 psi,sitting on the bike in a riding position and releasing the valve 60until air flow stops. Sag position can now be set without any additionalwork by the rider. As can be seen, such a procedure can greatly simplifyadjustment of sag over the currently available shock absorber designs.

In some embodiments, the valve 60 can include an internal valve 66 andthreads 68. The internal valve 66 can be positioned in fluidcommunication with a chamber 67. The internal valve 66 can be configuredto close the port 64 when the internal valve 66 is in a first position.The internal valve 66 can be backed out of the valve housing 70 to openthe port 64. This can help to ensure that the valve 60 remains securelyshut when in the first or closed position (FIG. 3) and can help toensure that the gas chamber 42 remains pressurized at the set pressure.Other configurations and types of valves are also possible. As mentionedpreviously, a Schrader valve or other type of valve can be used for thebleed down or air release operation. A Schrader valve can allow for bothfilling the valve and bleeding down, though the shock absorber canalternatively have a fill only valve, such as a valve near the eyelet(similar to FIG. 3A) and a bleed only type valve that can be used toadjust the final sag position.

In some embodiments, a shock absorber air pump can be used to bothincrease the pressure of the gas chamber 42 and release pressure, suchas releasing pressure until the piston 50 passes over the port 64.

A valve 60 can beneficially simplify sag setup for both end users andbike shops. A valve 60 can reduce setup time to achieve a desired sagposition. A valve 60 can reduce user error and increase repeatability.

Turning now to FIGS. 7-9 another embodiment of shock absorber 20′ isshown. As can be seen, shock absorber 20′ includes a bypass channel 82.The bypass channel 82 can be a groove along an inner surface of the gascylinder 44. For example, the groove can be a circumferential groove ora partially circumferential groove. The bypass channel 82 can be similarto the bypass channel described in particular in reference to FIGS. 3-5and the accompanying description at columns 5 and 6 in U.S. Pat. No.6,135,434, hereby incorporated by reference herein and made a part ofthis specification. The bypass channel 82 can permit fluid to bypass thepiston 50 to equalize the pressure in the gas cylinder 44 between thegas chamber 42 and the negative gas chamber 46.

According to certain embodiments, the sag position can be set in amanner similar to that described previously. The gas chamber 42 can becharged with gas, for example by a pump 80 (FIG. 7). The gas chamber 42can be over charged or over inflated to a pressure exceeding the finalpressure for a typical rider. A user can then mount the bicycle andwhile assuming a riding position, gas can be released from the shockabsorber through the valve 60.

As shown, gas can leave the gas chamber 42 until the piston 50 passesthe valve port 64 (FIG. 8). The negative gas chamber 46 can now equalizewith atmospheric pressure. After the valve is closed and the userdismounts the bicycle, the shock absorber 20′ will move back towards thetop out position of FIG. 7. In other words, as the load is removed fromthe shock absorber 20′, the shock will decompress and the piston 50 willmove back towards the initial position. As it does so, the piston 50will pass over the bypass 82. The bypass 82 will then permit fluid tobypass the piston 50 to equalize the pressure in the gas cylinder 44between the gas chamber 42 and the negative gas chamber 46 (FIG. 9).Thus, the negative gas chamber 46 can become charged with air pressure.Upon further movement of the piston as shown, the gas chamber 42 and thenegative gas chamber 46 again are sealed relative to one another.

The shock absorber 20′ can beneficially be used to automatically set thesag position based on an individual's weight and rider position. Theshock absorber 20′ and bypass 82 can advantageously be used to chargethe negative gas chamber 46. Having both the gas chamber 42 and thenegative gas chamber 46 charged can create an effective air spring onboth sides of the piston from the sag position. This can also result inbetter, more fluid movement of the shock absorber.

Although the preferred embodiment of the shock absorber illustrated inFIGS. 1 and 2 are used with the rear wheel of a bicycle, in otherpreferred embodiments, it may also be incorporated into the front wheelof the bicycle. Thus, the shock absorber may be a rear shock or a frontshock such as a front suspension fork.

Although this invention has been disclosed in the context of certainpreferred embodiments and examples, it will be understood by thoseskilled in the art that the present invention extends beyond thespecifically disclosed embodiments to other alternative embodimentsand/or uses of the invention and obvious modifications and equivalentsthereof. Additionally, it is contemplated that various aspects andfeatures of the invention described can be practiced separately,combined together, or substituted for one another, and that a variety ofcombination and sub-combinations of the features and aspects can be madeand still fall within the scope of the invention. Thus, it is intendedthat the scope of the present invention herein disclosed should not belimited by the particular disclosed embodiments described above, butshould be determined only by a fair reading of the claims.

What is claimed is:
 1. A bicycle assembly comprising: a shock absorbercomprising: a gas spring assembly; a movable piston being located withinthe gas spring assembly and dividing the gas spring assembly into afirst chamber having a first changeable volume and a second chamberhaving a second changeable volume; and at least one valve.
 2. A bicycleassembly comprising: a shock absorber comprising: a gas spring assembly;a movable piston being located within the gas spring assembly anddividing the gas spring assembly into a first chamber having a firstchangeable volume and a second chamber having a second changeablevolume; and at least one valve, the at least one valve being configuredto communicate with the first chamber when the movable piston is locatedin a first position and being configured to communicate with the secondchamber and not the first chamber when the movable piston is located ina second position other than the first position.
 3. A bicycle assemblycomprising: a shock absorber comprising: a gas spring assembly; amovable piston being located within the gas spring assembly and dividingthe gas spring assembly into a first chamber having a first changeablevolume and a second chamber having a second changeable volume; and atleast one valve; and a bypass chamber configured to permit fluid tobypass the moveable piston to equalize a first pressure in the firstchamber with a second pressure in the second chamber.